Alloy steel



Patented July 29, 1941 armor srcnr.

' Luciano G. Selmi, Detroit, and Clarence L. Altenlmrger, Deal-born,Mich, assignors to Great Lakes Steel Corporation, Ecorse, Mich, acorporation of Delaware No Drawing.

Application March 3, 1941,

Serial No. 381,560

4Claims.

The present invention relates to an alloy steel of the general nature ofthat set forth in our copending application, Serial No. 345,227, filedJuly 12, 1940 for Alloy steel.v The steel the said application is of thelow alloy type in that it comprises but small quantities-of alloyingmetals, or alloy elements, and yet has properties of high tensilestrength, deep drawing characteristics, high fatigue resistance andother important properties necessary for many uses of steels of thischaracter.

The general object of the present invention is to provide a steel whichmay be cheaply manufactured and which shall have some of the samecharacteristics as the steel of the aforementioned application and whichshall have, in addition, im-

- portant characteristics heretofore-obtained only in steels usinglarger quantities of alloying metals.

Such steels may thus be produced by the present invention at much lowercost than steels now on the market which have like characteristics.

More specifically steels heretofore manufactured, which have theproperties of high degree or high levels of hardness and capable ofvariable hardenability and also having important characteristics such asductility and machinability, have been made by including in the steelcomparatively large quantities of alloying elements. These elements are,by their very nature, expensive, and at the present time are becomingincreasingly diiiicult toobtain for commercial purposes.

Further specific objects therefore are to attain in an alloy steelcertain herein described desirable characteristics with the use of a lowpercentage of alloy elements.

As we have stated, a low alloy steel having many valuablecharacteristics i described and claimed in our above designatedcopending application. We have found that by maintaining certainrelationships between alloying elements, such an alloy steel may begiven unexpectedly difierent and highly desirable characteristics withonly minor changes in the percentages of the alloy elements. I

Further specific objects include a provision of a steel which shall beresistant to a very high velocity impact, resistant to shock andfragmentation, and which shall have permanent high cohesive strength. Itis desirable that the steel of the present invention shall have thishigh cohesive strength with a high ratio of such cohesive strength toits shear strength. Thus the steel is resistant to growth of andpropagation of cracks. Another object of the present invention is toSteels'now on the market having characteristic and properties such asare attained by our present invention, include alloying metals insubstantially high percentages-such for example as follows:

Nickel 1.75 Molyb n Chromium 75 Carbon 40 Manganese [70 Silicon 20Phosphorus, maximum .03 Sulphur, maximum .03 Aluminum lb. per ton 1 /2It will be seen that in the foregoing example of commercial steelcomparatively high percentages of these variable alloying elements havebeen heretofore considered essential to attain certain characteristics;We attain the essential characteristics of such a steel as willhereinafter appear with comparatively low percentages of such render asteel of this general nature highly resistant to quench alloying.elements as nickel and thus efiect marked economies.

With the low alloy metals of the percentages such as herein given,we-are enabled to provide a steel having an inherently fine grain and inwhich hardenability may be varied as desired through heretoforeunexpectedly wide ranges byrelatively small variations in the elements.Likewise we are able to provide a steel in which the hardenability maybe varied by small changes ofthe quenching temperatures. I

All of the above purposes and characteristics are attained within rangesof very much lower cost per ton.

Furthermore, we are enabled to maintain uniformity of product heretoforedifficult to obtain with anything comparable to our small percent-. agesof the alloying elements. S

As examples of steels made in accordance with the present invention andwhich have a wide variety of practical commercial uses which illustratesthe wide range in hardenability with small changes in the containedchemistry, that is, th alloyformula, we give the following: a

Steel A Steel B Steel A has a hardness in excess of 50 Rockwell C, alonga flat end quench bar up to V inch from the quenching endwhen quenchedfrom 1500" F.

Steel 3 has a hardness in excess of 50 Rockasasggaa well C along 2%inches or more from the quenched end when quenched from 1500 F.

In these examples, both steels are held at 1500 F. for one hour prior toquenching. Both are one inch round bars.

Steel A must be cooled at a rate in excess of 21 F. per second at 1250F. to harden above 50 Rockwell C, whereas in the example given for thesteel B, cooling may be as slow as about 2.7" F. per second through thetemperature of 1250 F. and still it will harden above the level of 50Rockwell C.

From the foregoing examples, it will be noted that the marked increaseddepth of hardenability of the steel B over the steel A accompanies theincrease of molybdenum. In the Example A, the molybdenum given is but atrace. In the Example B, molybdenum is given at 0.16%. Varying thisrange of molybdenum, while still maintaining it in within comparativelysmall quantity range, we have found our steels are hardenable throughgreat depths, and it is entirely practical within the range, say, of upto 0.35% molybdenum to harden locomotive or car axles throughout, that Vis, through thicknesses of six inches or more.

It will also be noted that the relative hardenability between our steelsA and B is accompanied with but slight changes in the other alloying'ele-- is slightly less than Example A; the manganese is slightlyhigher; the silicon is raised in the Ex- In particular reference tohardenability, widely I used steels such as having the first-givenformula, may have their quality of hardness varied only comparativelyslightly by widely varying the quenching temperatures.

With our present steel we may vary the levels of hardness through markedranges by slight variations in temperatures.

Steels, such as the example given, and others heretofore used, requirevariations in quenching temperatures of as high as 200 F. forcorrespond- 'ing results.

A steel such as steel A- may have its degree or levels of hardnessvaried materially by changes of as little as 20 degrees in quenchingtemperature, with shapes having comparatively thin or narrowcross-sections. The steel A may thus practically be treatedto attaindesired hardness levels throughout by variations of quenchingtemperatures through narrow ranges.

Examples of the efl'ects obtained by variation in cooling rates andquenching temperatures in the treating of steel 13 are tabulated belowas illustratlve. From these tables the increaseed hardenability effectedby change in temperatures and the resulting levels of hardness which wehave found are clearly apparent.

The left-hand column lists the diil'erences from the quenched end of thedepth or distance to which the hardness reaches. The second column givesthecooling rate of passing through the temperature of 1250 1". The thirdand fourth columns list Rockwell C hardness when quenched, usingtemperatures of 1475 F. and 1500 F, and after seventy-five minutes.

Rockwell 0 Distance Cooling rate mm F /sec at quenched quenched iz? 1250r. 1476" F. 15oo r.

after after min. 75 min.

Me 700 60 0034 it 450 60 60 9% 100 60% 60% ii 75 61 60 it 21 58% 58 ii14 58 56% l 8. 7 64 56% 1% 6 669i 1% 4 48 66 1% 3. 5 45% 56 2 3 45% 65 2l4 2. 7 44% 2% 2. 6 44% 53% 2% 2. 5 48 Steel B, in which more molybdenumis used, as for instance in the example given, is likewise responsive toslight changes in the quench temperature but its hardenabilitythroughout is governed more by the presence 0! molybdenum.

Examples of uses of alloy steels made in accordance with our presentinvention and which may be furnished at low cost compared to presentalloys used for like purposes are: automobile axles, gears, automobilesprings, airplane propellers, airplane engine shafts and many otherparts where exceptionally deep hardening is required such as, forexample, large axles for railway uses..

The expense or cost of the alloys for steels now used for a given weightor part may be several times that of steels made in accordance with ourpresent invention and having like win some respects superiorcharacteristics.

By the present invention, we have produced, as above indicated, aninherently fine grained, clean steel. It is substantially deoxidized andit is subject to controlling the degree and depth of its hardness.

A steel, suchas Example B, above-described, is highly resistant toquench cracking. It will withstand a drastic quench treatment such asthat of five percent caustic solution from above critical temperatures;for example, 1480 F. down to 32 F.

The steel has a balanced alloy composition and the relationship betweenthe molybdenum, when used, and theother elements, have surprisinglycritical characteristics accomplishing the objects as above set forth.

The oxydizing elements present in the steel are such as to produce lowdegrees of distortion during high heat treatment. The steel, unlikeother steels having comparable degrees of hardenability, has inherentproperties which result in a steel suitable for convenient and practicalfabrication such as forging and otherwise working. Our present steel hascharacteristics of weldability, that compare with alloys having likeproperties but which, as heretofore indicated. must have higherpercentages of other elements, such, for example, as nickel.

The example of the previous steels and examples of the two formulas ofour present alloy steel are given as illustrative, but it is understoodthat variation within reasonable elements may be made without departingfrom the scope of the present invention as defined in the appendedclaims.

We claim:

1. A steel having inherently fine grain and containing comparativelysmall quantities of alloy elements with hardenability variable throughwide ranges by relatively small variations of the alloy elements capableof being welded by commercial processes, and consisting of carbon .25-

..50 to 315%; silicon .70 to .90%; zirconium, .05

to .35%; molybdenum .05 to .25% and the balance iron. I

3. A steel having inherently fine grain and containing comparativelysmall quantities of aly elements in balanced ratios with hardenabilityvariable, ductile at high degree of hardness; resistant to quenchcracking, and consisting of carbon .40 to 55%; manganese .50 to .75%;

chromium .50 to 375%; silicon .70 to .90%; zirconium -.05 to 25%;molybdenum .05 to 20 and the remainder being iron.

4. A steel having a -hardness in excess of Rockwell C, having inherentlyfine grain and containing comparatively small quantities of alloyelements consisting of carbon .45%; manganese chromium 370%; silicon30%; zirconium .l5%; phosphorus .03% maximum; sulphur .03%

maximum; molybdenum about .15%, and the balance being iron, withhardenability variable through wide ranges by small variation ofquenching temperature.

' LUCIANO G. SELMI. I CLARENCE L. ALTENBURGER.

